Basic Specifications
The 6.7L Cummins (introduced mid-2007 in Dodge Ram 2500/3500 HD trucks) is a cast-iron inline-6 diesel built for power and emissions compliance. It displaces 6.7 liters/408 cubic inches with a bore of 4.21 in and stroke of 4.88 in. Fuel is delivered via a Bosch CP3 common-rail system (up to 26,000 psi), and boost comes from a Holset HE351VE variable-geometry turbocharger.
From day one the 6.7L Ram Cummins was equipped with emission hardware: it used exhaust gas recirculation (EGR) and a diesel particulate filter (DPF) to meet EPA regulations.
In stock form 2007.5 to 2010 Rams, the 6.7L is rated at 350 horsepower. Torque is 650 lb-ft with the automatic transmission and 610 lb-ft with the manual. These figures kept the Cummins competitive with Ford Powerstroke and GM Duramax diesels of the day. The engine has a 17.3:1 compression ratio and uses a deep-skirt gray-iron block with siamesed bores for strength. The cast-iron cylinder head and four-valve OHV design are similar to the older 5.9L Cummins, but every other aspect is upgraded (higher-pressure injection, turbo, exhaust brake, etc.).
Upgrades Over the Previous 5.9L Cummins
The 6.7L replaced the long-running 5.9L Cummins in mid-2007. The change was driven by stricter emissions rules effective in 2007, which the older engine could not meet. Increasing displacement to 6.7L was one strategy. The 6.7L’s bore and stroke are both larger than the 5.9L’s, yielding a 408 cu-in motor with significantly more torque at low RPM. The last 5.9L (2006 model) made up to 325 hp and 610 lb-ft, whereas the new 6.7L started at 350 hp/650 lb-ft. This required a beefier block: the 6.7L uses a reinforced, deep-skirt iron block with shared (“Siamese”) bores for the first and second cylinders to handle the extra torque. Equally important were the new “clean-diesel” technologies.
The 6.7L Cummins in Dodge was the first to feature both EGR and a DPF in one of these trucks. To meet NOx rules, hot exhaust gas is recirculated through a cooler (EGR), and soot is trapped in the DPF.
The 6.7L also got a fully electronic six-speed automatic (68RFE) that works with the Cummins’s exhaust brake. Fuel injection switched from the 5.9L’s VP44 pump to a high-pressure common rail (Bosch CP3) at 26,000 psi.
One side effect of the 6.7L’s upgrades was increased cylinder pressure. Because of the longer stroke, higher compression, and variable-geometry turbo (which produces strong low-RPM torque), the 6.7L’s head gasket runs hotter than the 5.9L’s. In practice, factory engines rarely failed until very high mileage, but it means heavy tuning or extreme towing can put extra strain on the top end.
In short, compared to the 5.9L the 6.7L added emissions hardware, advanced injection, and a sophisticated turbo, trading some reliability margin for much cleaner operation and higher output.
Reliability and Lifespan
In everyday use, the 6.7L Cummins is a robust and long-lived engine. Cummins specifies a B50 life of ~350,000 miles for the 6.7L (meaning half of these engines are expected to reach that many miles). A B10 life (10% failure) is about 250,000 miles. In the field, it is not uncommon to see well-kept 6.7L engines run 300k–400k miles with nothing more than routine servicing. Key to longevity is maintenance. The 6.7L’s wear items (oil pump, injectors, etc.) and emissions hardware (EGR, DPF) generally set the life limit, rather than internal mechanical failure. A stock 6.7L rarely gives major trouble before 200k miles if serviced properly.
Its iron block and head are very durable; the pushrod valvetrain and powdered-metal rods have proven reliable. The weakest links are usually the emissions systems and the intake grid heater (see below). Owners who delete or reinforce emission components often push life even further. Removing the DPF and EGR eliminates recurring regen cycles and hot gas recirculation, which in turn reduces thermal and mechanical stress. For example, many aftermarket shops recommend a DPF delete for any truck that sees heavy towing, so that the engine stays cleaner long-term. Likewise, adding head studs or upgrading to heavy-duty ones is a common “bulletproof” mod to prevent head lift. With such precautions, a 6.7L Cummins can run 400–500k miles with no internal rebuild.
In summary, the 2007.5–2009 6.7L Cummins is a reliable modern diesel. Its design life is around a quarter-million miles for most users, with many examples far exceeding that. Careful owners who follow service schedules (especially for oil and coolant) will find the engine can last as long as the chassis.
Common Problems with the 2007.5–2009 6.7L Cummins
Like any engine, the 07.5–09 6.7 Cummins has some known trouble spots. Fortunately, most of these are well understood and fixable:
EGR Cooler Failure
The EGR cooler’s job is to cool exhaust gases before they re-enter the engine. However, on the 6.7L these coolers can develop cracks or leaks. When the cooler fails, coolant leaks into the intake stream or combustion chamber. Typical symptoms are persistent white/gray exhaust smoke or steam, unexplained coolant loss, or cloudy oil. Owners and mechanics often misdiagnose this as a blown head gasket because coolant is entering cylinders. The only remedy is to replace the failed EGR cooler (and usually the EGR valve) – OEM coolers are expensive. Some trucks also benefit from upgraded EGR coolers or deletion kits. BulletProof Diesel, Spelab, EngineGo and similar makers sell “EGR delete” kits that block off the cooler, eliminating the failure point. But removing EGR means no emissions compliance in the street.
DPF (Diesel Particulate Filter) Clogging
The 6.7L’s factory DPF can clog over time, especially on 2007–2012 models, which had no DEF. The reason is that without DEF, the engine ran richer to meet NOx specs, producing more soot that the DPF must trap. Symptoms of a plug include loss of power, limp mode, frequent forced-regeneration cycles, or a dashboard warning light. Fixes include performing a high-temperature regen (passive or forced), having the DPF professionally cleaned with pressure washing, or outright replacing the DPF, which can cost $1,500–$2,500 for a new unit. A permanent solution some owners choose is a DPF delete, which involves removing the filter and installing a straight pipe plus an ECU tune. Delete kits sold by many diesel specialists prevent clogging entirely by bypassing the DPF.
Intake Heater Bolt Failure
The 6.7L Cummins has a notorious issue with the grid heater (an electric intake heater for cold starts). A small bolt secures the heater element’s electrical terminal, and over time this bolt corrodes or shears off. If it falls into the intake manifold, it will be drawn into the #6 cylinder, causing catastrophic damage. Such a failure will “completely [destroy] the piston, valve, and cylinder head” the vast majority of the time.
Often drivers get no warning; the first sign is usually engine noise or power loss as the bolt tears up the internals. There are some early warning codes: P2609 (“intake air heater voltage/performance”) and P0452 (an EVAP-related code often triggered by heater issues) signal that the grid heater bolt is losing conductivity.
Preventively, many owners upgrade or delete the grid heater: welding the bolt in place, installing a kit (e.g. BD Diesel’s grid-heater upgrade), or removing the heater entirely and plugging the intake. If you do get a grid heater failure (hear grinding or see bolt fragments), the engine usually requires a top-end rebuild.
Oil (Fuel) Dilution
Because the 6.7L 2007–2012 does regen by injecting extra fuel, some unburned diesel can end up in the crankcase. The injectors squirt fuel into the exhaust stroke to burn soot, so some excess fuel can stick to the cylinder wall where it’s then picked up by the oil.
Cummins considers about 5% diesel-in-oil normal for these engines. However, higher levels of dilution thin the oil and reduce lubrication. The symptoms of fuel dilution are milky oil (from fuel) and a lower oil level.
To combat this, it’s important to change the oil on schedule (often more frequently than gasoline trucks). Some owners use an aftermarket engine tune that slightly alters the regen strategy, but the only surefire way to eliminate dilution is a DPF delete (since deleting the DPF means no extra fuel is needed in the exhaust).
Head Gasket Issues
The 6.7L’s higher torque can stress the head gasket, making head gasket leaks a relatively common high-mileage issue. The symptoms of a leaking head gasket include white exhaust smoke, coolant loss, engine overheating, or milky oil (coolant mixing with oil). Unlike a sudden head gasket blowout, 6.7Ls often show gradual leaks.
Any consistent overheat or coolant drop should be inspected, as a failing gasket can warp the head. Repair involves removing the head, inspecting for warpage/cracks, and installing a new OE head gasket using proper torque sequence and even better, upgraded head studs. It’s worth mentioning that the 6.7L head bolts are 12-point and not as strong as aftermarket studs; many Cummins builders use ARP studs when refreshing the head.
In practice, head gasket jobs become more common after 200–250k miles, or if the engine overheats, but are not normally seen at low mileage. Keeping the cooling system in good order (proper coolant, no air pockets) helps delay this issue.
Turbocharger Problems
The variable-geometry turbo (VGT) on the 6.7L is durable but has a few failure modes:
Bearing wear: After roughly 100,000+ miles, the turbo’s journal bearings can wear. When this happens, drivers often hear a high-pitched whistle or grinding noise from the turbo. A failing turbo can grind metal on metal, and pieces of it can enter the engine. The cure is to rebuild or replace the turbo. Many owners upgrade to modern turbos (ball-bearing designs) from BD Diesel, Fleece, or others for longevity.
Shaft seal leaks: If the turbo’s seals leak oil, you’ll notice blue smoke on startup or heavy boost. This indicates turbo oil seal failure and means the turbo must be serviced or replaced.
VGT vane/actuator issues: The VGT mechanism can get stuck from soot, or the electronic actuator can fail. Symptoms include erratic boost or turbo fault codes. Notably, in 2009 Dodge added an access port for cleaning the VGT vanes without removing the turbo. Periodic cleaning of the VGT vanes is recommended on high-mileage trucks. If the actuator motor fails, the turbo might need replacement.
In summary, the 6.7L’s turbo usually fails from normal bearing wear or actuator problems. A turbo that whines or smokes should be repaired promptly. Upgrading to a higher-capacity or non-VGT turbo is a common modification for extra reliability and power.
Overall, these common issues – EGR, DPF, grid heater, and so on – are mostly tied to emissions controls. The Cummins block and bottom end are otherwise very strong. Owners often simply delete or upgrade the problematic emissions parts to eliminate these failure points, as discussed next.
How to Improve 2007.5–2009 Cummins Reliability (Deletes & Upgrades)
To maximize reliability of these trucks, many owners perform preventative mods that eliminate known failure points. Popular measures include:
- DPF Delete: Removing the diesel particulate filter (and installing a straight pipe or race pipe exhaust) eliminates the risk of DPF clogging. Without a DPF, the truck will never need regen cycles, so no soot is burned in the exhaust. This also stops fuel dilution and reduces engine stress. Of course, this requires a tune or module to clear DPF codes.
- EGR Delete: Installing an EGR delete kit (block-off plates and intake gaskets) removes the EGR cooler and valve from the system. With no EGR, no hot exhaust enters the intake, so the cooler can’t fail and no soot enters the engine.
- CCV Reroute/Delete: The closed-crankcase ventilation (CCV) filter on the 6.7L can clog and cause pressurization and oil leaks. A CCV reroute kit vents crankcase fumes out of the engine instead of through the factory filter. Deleting the CCV filter entirely is a simple mod that prevents the filter from ever clogging. This reduces oil leaks and venting issues. Ram recommends changing the CCV filter ~67,500 miles, but many owners find it clogs closer to 40–50k under heavy use.
- Grid Heater Delete/Upgrade: Replacing the fragile bolt or deleting the intake grid heater eliminates that failure mode. The BD Diesel “Killer Grid Heater” kit, for example, replaces the bolt/terminal with a soldered bar and stronger fasteners. Some opt to remove the heater entirely and install a plate (along with plugging the plumbing).
- Head Studs and Upgrades: When doing a top-end rebuild or preemptively, many install ARP head studs instead of stock bolts. This prevents head gasket lift under extreme pressure, which is helpful if towing or tuning. A stronger oil cooler, water pump, or thermostat can also be fitted to improve cooling.
- Turbo Upgrades: Replacing the weak OEM turbo with a beefier unit or an aftermarket VGT with better bearings improves reliability. Non-VGT turbos can also be used to avoid vane issues.
- Regular Maintenance: Finally, keep up with oil changes, using high-quality synthetic oil, replace injectors and fuel filter on schedule, and inspect coolant/EGR systems routinely. Use the correct Cummins coolant and never let the truck run hot. Properly torquing head bolts and checking valve lash every 150k mi helps the engine stay trouble-free.
By proactively deleting or reinforcing weak points, 2007.5–2009 6.7L Cummins owners can dramatically reduce unscheduled repairs. In effect, these mods remove the common failure components so the engine only has to concern itself with core mechanical durability. The products linked at here (DPF delete pipes, EGR block-offs, CCV kits, etc.) can be useful resources to implement these upgrades.
Which 2007.5–2009 Dodge Ram 6.7L Cummins Model Year Is the Best?
From 2007.5 through 2009, Dodge’s heavy-duty Rams all used the same generation of the 6.7L Cummins with identical engine hardware. There were no big changes in output or design between these years. Minor improvements were made: for example, 2009 models received small service updates such as an easier turbo vane cleaning port, an updated fuel filter housing, and even a chassis upgrade (2009 Rams got a revamped steering linkage to fix the “death wobble” issue). But mechanically the engines were unchanged.
As a result, there is no single “best” year purely for the engine. Any 2007.5–2009 truck can be equally reliable if properly maintained. Some buyers prefer a 2009 Ram simply because it’s the latest in that range (with all minor fixes applied) and typically has a bit more options on the truck. Others may lean toward 2008 if a particularly low-mileage example is available. The bottom line is to judge the purchase by the truck’s condition, not the model year. A well-cared-for 2007.5 with full service records will be better than a neglected 2009. In this year range, look for trucks that have had their DPF cleaned, the coolant system flushed on schedule, and no persistent check-engine lights. All else equal, 2009 had the refinement advantage and by then owners had learned the common 6.7L quirks. But engine-wise, 07.5, 08, and 09 are very similar. Choose the nicest truck you can find, and you’ll have the best 6.7L Cummins of that generation.
Conclusion
Overall, the 2007.5–2009 6.7L Cummins combines modern clean‑diesel technology with robust mechanical design, delivering 350 hp and 650 lb‑ft in a durable cast‑iron package. While EGR, DPF, grid heater bolts, and turbo components can require attention over high mileage, proactive maintenance and targeted deletes or upgrades greatly enhance reliability. By understanding common failure modes and implementing preventative mods, owners can confidently achieve 300k‑plus miles and maximize the performance and longevity of their Cummins‑powered Rams.
FAQ
- What year did the Ram 2500/3500 with the 6.7L Cummins come out?
The 6.7L Cummins debuted in Ram trucks for the 2007 model year, introduced mid-2007 (often called 2007.5). That year’s Ram pickups were the first to drop the old 5.9L for the new 6.7L, in order to meet stricter emissions regulations.
- What is the fuel mileage for a Ram 6.7L Cummins diesel?
Real-world fuel economy for a 6.7L Ram is generally in the low-to-mid teens MPG. For example, aggregated owner data shows a 2008 Ram 2500 (6.7L diesel, auto) averages about 13.9 MPG combined. Highway numbers in good conditions can reach the upper teens (15–18 MPG), but city or towing can drop into the low teens or worse. Factors like load, driving speed, and weather have big effects. In short, plan on roughly 14 MPG on average, with better mileage on open highway and lower mileage in town or towing.
- How much horsepower does a 6.7L Cummins have?
The 2007.5–2010 6.7L Cummins is factory-rated at 350 hp. In a Ram 2500/3500, that 350 hp comes at about 3,000 rpm. The torque rating is 650 lb-ft with the six-speed automatic; manual-transmission trucks were rated at about 610 lb-ft. These are the same ratings for all 2007.5–2009 Rams with that engine. Later in 2011–2012 the automatic models jumped to 800 lb-ft, but that was in the next model phase.
